Artifact eff68e3f257e05e81eae6c4d50a51eb88beb4ff3:

File
src/random.c
— part of check-in
[8af6474c]
at
2004-05-08 08:23:20
on branch trunk
— Change lots of internal symbols from sqliteXXX to sqlite3XXX so that the
library links again. It doesn't work yet, due to changes in the btree layer
calling convention. (CVS 1324)
(user:
danielk1977
size: 2945)

/*
** 2001 September 15
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains code to implement a pseudo-random number
** generator (PRNG) for SQLite.
**
** Random numbers are used by some of the database backends in order
** to generate random integer keys for tables or random filenames.
**
** $Id: random.c,v 1.12 2004/05/08 08:23:32 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include "os.h"
/*
** Get a single 8-bit random value from the RC4 PRNG. The Mutex
** must be held while executing this routine.
**
** Why not just use a library random generator like lrand48() for this?
** Because the OP_NewRecno opcode in the VDBE depends on having a very
** good source of random numbers. The lrand48() library function may
** well be good enough. But maybe not. Or maybe lrand48() has some
** subtle problems on some systems that could cause problems. It is hard
** to know. To minimize the risk of problems due to bad lrand48()
** implementations, SQLite uses this random number generator based
** on RC4, which we know works very well.
*/
static int randomByte(){
unsigned char t;
/* All threads share a single random number generator.
** This structure is the current state of the generator.
*/
static struct {
unsigned char isInit; /* True if initialized */
unsigned char i, j; /* State variables */
unsigned char s[256]; /* State variables */
} prng;
/* Initialize the state of the random number generator once,
** the first time this routine is called. The seed value does
** not need to contain a lot of randomness since we are not
** trying to do secure encryption or anything like that...
**
** Nothing in this file or anywhere else in SQLite does any kind of
** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random
** number generator) not as an encryption device.
*/
if( !prng.isInit ){
int i;
char k[256];
prng.j = 0;
prng.i = 0;
sqlite3OsRandomSeed(k);
for(i=0; i<256; i++){
prng.s[i] = i;
}
for(i=0; i<256; i++){
prng.j += prng.s[i] + k[i];
t = prng.s[prng.j];
prng.s[prng.j] = prng.s[i];
prng.s[i] = t;
}
prng.isInit = 1;
}
/* Generate and return single random byte
*/
prng.i++;
t = prng.s[prng.i];
prng.j += t;
prng.s[prng.i] = prng.s[prng.j];
prng.s[prng.j] = t;
t += prng.s[prng.i];
return prng.s[t];
}
/*
** Return N random bytes.
*/
void sqlite3Randomness(int N, void *pBuf){
unsigned char *zBuf = pBuf;
sqlite3OsEnterMutex();
while( N-- ){
*(zBuf++) = randomByte();
}
sqlite3OsLeaveMutex();
}

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